摘要:

Three new approximants to the solution of the one‐dimensional nonlinear Debye screening potential have been obtained. The ions and electrons are in steady‐state equilibrium situations with different temperatures. Therefore, the potential satisfies the nonlinear Poisson equation with a Boltzmann factor for both the electronic and ion densities. To obtain the approximants, the original equation has been written in a suitable compact way. The variables have been transformed in such a way that the two‐point quasifractional approximation technique can be applied. The simplest approximant is almost as simple as the usual linear one, but it has an additional coefficient and it is more accurate. The other two approximants, more accurate than the simplest one, are exact for the limit of equal temperatures. All the approximants obtained here give better accuracy than the third‐order approximation obtained previously by Clemente and Marti´n [J. Phys. Soc. Jpn.61, 34 (1992)].  

ISSN:1070-664X    

DOI:10.1063/1.870607

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The polarization force on a charged particulate or ‘‘dust’’ grain in a nonuniform plasma with finite ion flows and an external electric field is derived, based on a fluid approximation for the background plasma. This polarization force is proportional to the magnitude of the spatial gradient of the Debye length, and acts in the direction of decreasing Debye length. When the ion flow velocity is sufficiently large compared to ion thermal velocities, ions do not participate in the formation of sheaths around negatively charged particulates and the electron Debye length must be employed, since sheaths comprise only a deficiency of electrons. If the ion flow velocity is small, the contribution of the ion flow to the polarization force is proportional to the spatial gradient of the flow kinetic energy and is thus usually negligible. The expressions describing the plasma–particulate interaction may be applied to the modeling of contaminant behavior in materials‐processing plasmas.

ISSN:1070-664X    

DOI:10.1063/1.870608

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Using the relativistic Vlasov equation and the appropriate Maxwell–Boltzmann–Ju¨ttner distribution for the unperturbed plasma thermal equilibrium state, it is demonstrated that the longitudinal dispersion relation in warm isotropic Maxwellian plasmas has two real roots with superluminal phase speed below a characteristic wave numberkcthat is determined by the plasma frequency and the plasma temperature. The superluminal oscillations undergo no Landau damping. The relativistically correct analysis leads to markedly different results than previous nonrelativistic work which incorrectly yielded a nonzero imaginary part of the roots for all phase speeds.

ISSN:1070-664X    

DOI:10.1063/1.870609

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A plasma vortex street configuration can evolve when two velocity and one magnetic shear layer interact strongly. A study of the interaction between two‐ and three‐dimensional plasma modes and a mean sheared magnetic field is undertaken using a three‐dimensional magnetohydrodynamic spectral Galerkin computation. The initial state is a simple magnetic shear in a plane perpendicular to the plasma velocity shear plane. In a very weak magnetic field, secondary instabilities (three‐dimensional modes), expressed by the kinking of vortex tubes, lead to plasma flow along and around the axes of the vortex cores, creating characteristic patterns of kinetic helicity and linkages between vortex filaments. Three‐dimensionality leads to the vortex breakdown process. A strong sheared magnetic field inhibits the kinking of vortex tubes, maintaining two‐dimensionality. This inhibits vortex breakdown over long dynamical times. There is an anticorrelation in time between linkage indices of the vortex filament (related to kinetic helicity), suggesting that the ellipticity axes of the vortex cores along the street undergo a global inphase evolution. This anticorrelation has a dynamical interpretation. It extends to a relaxing plasma in the Navier–Stokes flow notion that helical regions of opposite helicities interact and screen each other off so that the global helicity remains bounded.

ISSN:1070-664X    

DOI:10.1063/1.870610

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A set of reduced Braginskii equations is derived without assuming flute ordering and the Boussinesq approximation. These model equations conserve the physical energy. It is crucial at finite &bgr; that the perpendicular component of Ohm’s law be solved to ensure∇⋅j=0 for energy conservation.

ISSN:1070-664X    

DOI:10.1063/1.870611

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The weakly nonlinear theory of two‐dimensional electron drift modes is outlined and a double energy cascade is demonstrated, due to the presence of two rugged invariants. Statistical equilibrium spectra of the fully and weakly nonlinear systems are calculated using a discrete Fourier mode phase space and Hopf’s equation. A Monte Carlo simulation based on the weakly nonlinear theory gives a detailed energy spectrum with several similarity ranges, suggesting the existence of an approximate additional local (inkspace) quadratic invariant. The inhomogeneity of the underlying system is reflected by spectral anisotropy. Some general problems of statistical fluid mechanics are discussed.

ISSN:1070-664X    

DOI:10.1063/1.870612

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Effect of ion temperature on the conditions for existence of solitary waves in a relativistic plasma is studied using Sagdeev’s pseudopotential approach. It is shown that the ion temperature puts a restriction on the values ofV, the soliton velocity. It is also shown that for small amplitude and cold ions, the present results agree with the existing published results. Numerical solutions of the equation of motion derived from the pseudopotential are obtained to see the effect of ion temperature on the width and amplitude of the ion‐acoustic solitary waves.  

ISSN:1070-664X    

DOI:10.1063/1.870613

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Large amplitude Langmuir and ion‐acoustic waves in a weakly relativistic two‐fluid plasma are analyzed by the pseudopotential method. The existence conditions for relativistic nonlinear Langmuir waves depend on the relativistic effect, the particular energy, and the ion mass to electron mass ratio. The allowable range of the normalized potential depends on the relativistic effect. It is shown that the Mach number has the significant effect for the formation of relativistic nonlinear ion‐acoustic waves rather than the ratio of the ion‐acoustic velocity to the velocity of light. The allowable range of the normalized potential depends on the Mach number. The present investigation predicts new findings of relativistic nonlinear Langmuir and ion‐acoustic waves in plasmas in which high‐speed electrons and ions coexist.

ISSN:1070-664X    

DOI:10.1063/1.870614

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Whistler wave excitation in a magnetized laboratory plasma by a density modulated electron beam is studied for frequency modulation below, but in the range of, the electron gyrofrequency. When the beam velocity differs from the phase velocity of the whistler at the frequency modulation of the beam, a whistler wave, and, by Cˇerenkov emission, a beam wave at the same frequency are excited as single poles. When both velocities are equal, a resonance occurs leading to a maximum in the emission of whistler waves. The experiment performed in a magnetized plasma (np≊1011cm−3,Te≊0.2 eV,B≊100 G) with a modulated electron beam (nb≊109cm−3,Eb≊300 eV) is in agreement with a simple model which predicts the characteristics of the excited waves.

ISSN:1070-664X    

DOI:10.1063/1.870615

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Ion‐acoustic solitary waves in a warm, magnetoplasma under the initial drift motion of the electrons in the direction of the magnetic field, have been investigated. It has been established that both compressive and rarefactive solitons exist within the parametric domains. For higher (lower) values of the electron drift velocityve’, it is demonstrated that the solitary wave is always subsonic (supersonic) near the lower regime of &agr; (=Ti/Te, the ion to electron temperature ratio) and upper regime of &agr;, respectively. It is of paramount importance to report that a higher and constant amplitude soliton region corresponding to low ion temperature and Mach numberMexists for the upper ranged values ofve’but to the contrary a smaller and constant amplitude soliton region exists corresponding to high ion temperature for the lower ranged values ofve’.

ISSN:1070-664X    

DOI:10.1063/1.870616

出版商:AIP    

年代:1994

数据来源: AIP